Now a clearly identified phenomenon, a major depressive episode at menopause can cause extensive morbidity and mortality. Its pathogenesis and treatment, however, have not been systematically investigated. Medical studies have focused on the cardiovascular and reproductive systems, with relatively little attention being paid to the central nervous system. We have observed increased melatonin secretion and delayed morning offset in menopausal depressed patients (DP) compared with normal control (NC) women. The aim of this revised application is to test the hypothesis that compared with NC women, menopausal DP have increased melatonin amplitude and delayed morning offset, attributable primarily to alterations in a) light/dark and sleep/wake cycles and b) reproductive and other endocrine functions. According to our conceptual model, menopausal DP have a decreased hypothalamic sensitivity to gonadal steroids, which disrupts the normal regulation of circadian rhythms, and is manifested in increased melatonin secretion with delayed morning offset. Increased arousals in dim light at night, resulting in delayed wake time with decreased and delayed exposure to morning bright light, increased daytime sleep or insufficient or decreased sensitivity to light exposure, exacerbate the problem. Reminiscent of the findings in hamsters during extended dark periods at night in winter, menopausal DP have increased melatonin duration, extended sleep time, recent hypogonadism, higher Follicle Stimulating Hormone (FSH) levels and Body Mass Index (BMI) that correlate with depression ratings. Our aim in this proposal is to extend and replicate our preliminary findings of abnormal melatonin secretion in menopausal DP and investigate the likely contributing factors of light, sleep, activity and reproductive endocrine function, as a basis for developing treatments targeted to specific pathogenic factors in future studies. In 50 peri- or post-menopausal DP by DSM-IV criteria, and in 50 NC women, matched for age and menopausal status, we will measure the phase, amplitude, waveform and temporal relations among 24-hour cycles of plasma melatonin (30 minute sampling in dim light), illumination, sleep and activity (by polysomnography and Actillume), as well as reproductive endocrine function (by gonadotropin and steroid levels) and BMI, in relation to mood. As an extension of our ongoing investigation of the chronobiology of premenstrual, pregnancy and postpartum depression, this study has the potential to lead to the development of new hypotheses and treatment strategies. The findings may impact the understanding of other depressive disorders related to the reproductive cycle in women. It also will confirm and extend our understanding of chronobiological abnormalities in depressed women as the basis for developing innovative treatments.